By Elias GrollElias Groll is a staff writer at Foreign Policy, covering cyberspace and its conflicts and controversies. He has written for the magazine since 2012 and is a graduate of Harvard University.

In a perplexing series of Friday-morning tweets, President Donald Trump appeared to confirm that he is under investigation by the FBI and leveled a scathing attack against the officials leading the inquiry.

Trump appeared to be responding to reports this week that the FBI is investigating Trump’s decision to fire FBI Director James Comey and his apparent attempts to quash the bureau’s investigation of former National Security Advisor Michael Flynn.

Comey has claimed Trump asked him to drop the investigation when he was heading the bureau, and according to multiple media reports, Trump attempted to enlist several senior intelligence official in a campaign to discredit the investigation and to state publicly that Trump did not collude with the Russian campaign to boost his electoral chances.

The federal investigation led by special counsel Robert Mueller, a former FBI director, is reportedly examining whether Trump’s actions rise to the level of obstruction of justice. If Trump is confirming the existence of an investigation targeting him, it would represent an extraordinary development less than five months into his presidency.

Trump’s 9:07 a.m. tweet appeared to be principally directed at Deputy Attorney General Rod Rosenstein, the No. 2 official at the Justice Department who authored a memo justifying Comey’s firing.

While Rosenstein has some supervisory responsibilities for the FBI’s investigation of Russian meddling in the 2016 election and whether any Trump aides conspired with that campaign, the probe is being led by Mueller, the special counsel Rosenstein appointed in the wake of Comey’s firing. The special counsel can only be fired by Rosenstein, though the president could in in theory direct Rosenstein to fire him.

Rosenstein pledged this week that he would maintain the integrity of the investigation and saw no reason to fire Mueller, despite reports that Trump was considering such a move.

Before Trump took to Twitter on Friday, Rosenstein on Thursday issued a perplexing statement of his own, denouncing news stories based on anonymous sources. “Americans should exercise caution before accepting as true any stories attributed to anonymous ‘officials,’ particularly when they do not identify the country — let alone the branch or agency of government — with which the alleged sources supposedly are affiliated,” Rosenstein said late Thursday. “Americans should be skeptical about anonymous allegations. The Department of Justice has a long-established policy to neither confirm nor deny such allegations.”